If you saw a banner ad today, there’s a good chance it was from a travel company. The industry is recovering as the country moves away from the recession, and airlines, hotels and rental car companies want to claim their share of your cash. To reach into your wallet, these guys are moving online, and they’re spending a boatload of bucks.

Unsurprisingly, the retail sector leads the world in online ad spending, pumping $5.16 billion into it last year – with an expected $5.73 billion to come in 2011. That’s good for 20 percent of the online ad market in 2010 and 2011. The travel industry is a lot smaller. It spent $1.81 billion last year to capture 5.6 percent of online advertising spend. In 2011, eMarketer expects travel companies to push their investments higher, with online ad spending forecasted to reach a whopping $1.95 billion.

You know what’s funny? In 2010, travel companies were responsible for 7 percent of online ad spending in the United States, but the extra $1.4 billion coming this year isn’t good enough to keep that level. In 2011, travel’s share of the online advertising pie will drop to 6.8 percent, according to the eMarketer estimates.

So, what should you take from this?

Travel companies are looking for growth. The market is coming back, and travelers are taking to the road again. Improved service and additional routes are nice, but it’s also important to get in front of potential buyers. After all, we know what kind of wheel gets the grease!